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Stowaway wrecks island’s crops

By Fred Pearce

A PINK bug never before seen in the western hemisphere is destroying the vegetation and crops of Grenada, and threatens to run amok through the Caribbean and beyond. Alleged by some to have arrived in the diplomatic bag of the Taiwanese mission in St George’s, the Grenadian capital, the pink mealybug has attacked more than a hundred species of trees and crops in the past two years.

“It’s a natural disaster. The whole island is being defoliated. There will probably be no cocoa crop at all this year,” says Matthew Cock of the International Institute of Biological Control in Ascot, Berkshire. Cock, who has just returned from the island, is masterminding a war against the bug using one of its natural predators, a parasitic wasp.

The 2-millimetre-long mealybug, Maconellicoccus hirsurus, has already hopped from island to island hidden in cargoes of food. It reached Trinidad in August, St Kitts in October, and unconfirmed reports say that it is in Nevis and the Venezuelan island of Margarita, as well as Guyana on the South American mainland. Next stop, says Cock, could be Dominica, where the island’s main crop, bananas, would be under threat. “The whole Caribbean basin is at risk.”

The bug is undermining the economy of Grenada, one of the poorest islands in the Caribbean. The government estimates the damage for 1995 at &dollar;60 million, almost a quarter of its GDP. “Many of Grenada’s 15 000 small farmers are now without an income, and domestic food prices are increasing,” says John Magrath of Oxfam, who calls the invasion an “impending regional disaster”. Cocoa, okra and sorrel crops have all been destroyed.

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Trees attacked by the mealybug include teak, blue mahoe, saman and hibiscus. One of the island’s main watersheds, Les Avocats, has lost most of its blue mahoe. Most of the island’s saman trees are dead and most of its teak trees have no foliage. The country’s nutmeg crop, source of a quarter of the world’s nutmeg, is one of the few crops left untouched.

The outbreak has strong parallels with the spread of another alien species of mealybug, which escaped from Latin America to the cassava fields of Central and West Africa in the 1970s and 1980s. Poor African farmers lost crops worth millions of dollars before scientists introduced a South American predator to bring it under control. In both this and the Grenadian case, the bug arrived accidentally, but unaccompanied by any of the wasps that prey on it and make it largely innocuous at home.

The African outbreak was beaten by the introduction of a parasitic wasp from Paraguay, which laid its eggs in the mealybug, a technique which won its inventor the World Food Prize last year. The Grenadian authorities have so far attempted to fight the pink mealybug with pesticides and by cutting down and burning infected plants and trees. But this strategy has not worked, says Cock, and hope now hangs on biological pest control.

Last summer, Cock identified a Chinese parasitic wasp, Anagyrus kamali, as a natural predator of the pink mealybug. “We have brought wasps back to Britain for quarantining to ensure a clean culture, and sent them on to Grenada for culturing,” says Cock. “The first few hundred wasps were released in Grenada last month and Trinidad will follow next month. A few thousand wasps may be enough, but we shall see.”